Background S-Nitrosoglutathione (GSNO) is the S-nitrosated derivative of glutathione and is thought to be a critical mediator of the down-stream signaling effects of nitric oxide (NO). GSNO has also been implicated as a contributor to various disease states. Scope of Review This review focuses on the chemical nature of GSNO, its biological activities, the evidence that it is an endogenous mediator of NO action, and implications for therapeutic use. Major Conclusions GSNO clearly exerts its cellular actions through both NO- and S-nitrosation-dependent mechanisms; however, the chemical and biological aspects of this compound should be placed in the context of S-nitrosation as a whole. General Significance GSNO is a central intermediate in formation and degradation of cellular S-nitrosothiols with potential therapeutic applications; thus, it remains an important molecule of study.

Type 1 diabetes (T1D) is a T cell–mediated autoimmune disease characterized by the destruction of insulin-secreting pancreatic β cells. In humans with T1D and in nonobese diabetic (NOD) mice (a murine model for human T1D), autoreactive T cells cause β-cell destruction, as transfer or deletion of these cells induces or prevents disease, respectively. CD4+ and CD8+ T cells use distinct effector mechanisms and act at different stages throughout T1D to fuel pancreatic β-cell destruction and disease pathogenesis. While these adaptive immune cells employ distinct mechanisms for β-cell destruction, one central means for enhancing their autoreactivity is by the secretion of proinflammatory cytokines, such as IFN-γ, TNF-α, and IL-1. In addition to their production by diabetogenic T cells, proinflammatory cytokines are induced by reactive oxygen species (ROS) via redox-dependent signaling pathways. Highly reactive molecules, proinflammatory cytokines are produced upon lymphocyte infiltration into pancreatic islets and induce disease pathogenicity by directly killing β cells, which characteristically possess low levels of antioxidant defense enzymes. In addition to β-cell destruction, proinflammatory cytokines are necessary for efficient adaptive immune maturation, and in the context of T1D they exacerbate autoimmunity by intensifying adaptive immune responses. The first half of this review discusses the mechanisms by which autoreactive T cells induce T1D pathogenesis and the importance of ROS for efficient adaptive immune activation, which, in the context of T1D, exacerbates autoimmunity. The second half provides a comprehensive and detailed analysis of (1) the mechanisms by which cytokines such as IL-1 and IFN-γ influence islet insulin secretion and apoptosis and (2) the key free radicals and transcription factors that control these processes.

Significance: S-nitrosothiol formation and protein S-nitrosation is an important nitric oxide (NO)-dependent signaling paradigm that is relevant to almost all aspects of cell biology, from proliferation, to homeostasis, to programmed cell death. However, the mechanisms by which S-nitrosothiols are formed are still largely unknown, and there are gaps of understanding between the known chemical biology of S-nitrosothiols and their reported functions. Recent Advances: This review attempts to describe the biological chemistry of S-nitrosation and to point out where the challenges lie in matching the known chemical biology of these compounds with their reported functions. The review will detail new discoveries concerning the mechanisms of the formation of Snitrosothiols in biological systems. Critical Issues: Although S-nitrosothiols may be formed with some degree of specificity on particular protein thiols, through un-catalyzed chemistry, and mechanisms for their degradation and redistribution are present, these processes are not sufficient to explain the vast array of specific and targeted responses of NO that have been attributed to S-nitrosation. Elements of catalysis have been discovered in the formation, distribution, and metabolism of S-nitrosothiols, but it is less clear whether these represent a specific network for targeted NO-dependent signaling. Future Directions: Much recent work has uncovered new targets for S-nitrosation through either targeted or proteome-wide approaches There is a need to understand which of these modifications represent concerted and targeted signaling processes and which is an inevitable consequence of living with NO. There is still much to be learned about how NO transduces signals in cells and the role played by protein S-nitrosation. Antioxid. Redox Signal. 17, 969-980.

Recent studies have highlighted the fact that cancer cells have an altered metabolic phenotype, and this metabolic reprogramming is required to drive biosynthesis pathways necessary for rapid replication and proliferation. Specifically, the importance of tricarboxylic acid (TCA) cycle-generated intermediates in the regulation of cancer cells proliferation has been recently appreciated. One function of monocarboxylate transporters (MCTs) is to transport the TCA cycle substrate pyruvate across the plasma membrane and into mitochondria, and inhibition of MCTs has been proposed as a therapeutic strategy to target metabolic pathways in cancer. Here, we examined the effect of different metabolic substrates (glucose and pyruvate) on mitochondrial function and proliferation in breast cancer cells. We demonstrated that cancer cells proliferate more rapidly in the presence of exogenous pyruvate when compared to lactate. Pyruvate supplementation fueled mitochondrial oxygen consumption and the reserve respiratory capacity, and this increase in mitochondrial function correlated with proliferative potential. In addition, inhibition of cellular pyruvate uptake using the MCT inhibitor α-cyano-4-hydroxycinnamic acid impaired mitochondrial respiration and decreased cell growth. These data demonstrate the importance of mitochondrial metabolism in proliferative responses and highlight a novel mechanism of action for MCT inhibitors through suppression of pyruvate-fueled mitochondrial respiration.

SummaryMitochondrial changes have long been implicated in the pathogenesis of Parkinson's disease (PD). The glycine to serine mutation (G2019S) in leucine-rich repeat kinase 2 (LRRK2) is the most common genetic cause for PD and has been shown to impair mitochondrial function and morphology in multiple model systems. We analyzed mitochondrial function in LRRK2 G2019S induced pluripotent stem cell (iPSC)-derived neurons to determine whether the G2019S mutation elicits similar mitochondrial deficits among central and peripheral nervous system neuron subtypes. LRRK2 G2019S iPSC-derived dopaminergic neuron cultures displayed unique abnormalities in mitochondrial distribution and trafficking, which corresponded to reduced sirtuin deacetylase activity and nicotinamide adenine dinucleotide levels despite increased sirtuin levels. These data indicate that mitochondrial deficits in the context of LRRK2 G2019S are not a global phenomenon and point to distinct sirtuin and bioenergetic deficiencies intrinsic to dopaminergic neurons, which may underlie dopaminergic neuron loss in PD.

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c Nitric oxide, produced in pancreatic ␤ cells in response to proinflammatory cytokines, plays a dual role in the regulation of ␤-cell fate. While nitric oxide induces cellular damage and impairs ␤-cell function, it also promotes ␤-cell survival through activation of protective pathways that promote ␤-cell recovery. In this study, we identify a novel mechanism in which nitric oxide prevents ␤-cell apoptosis by attenuating the DNA damage response (DDR). Nitric oxide suppresses activation of the DDR (as measured by ␥H2AX formation and the phosphorylation of KAP1 and p53) in response to multiple genotoxic agents, including camptothecin, H 2 O 2 , and nitric oxide itself, despite the presence of DNA damage. While camptothecin and H 2 O 2 both induce DDR activation, nitric oxide suppresses only camptothecin-induced apoptosis and not H 2 O 2 -induced necrosis. The ability of nitric oxide to suppress the DDR appears to be selective for pancreatic ␤ cells, as nitric oxide fails to inhibit DDR signaling in macrophages, hepatocytes, and fibroblasts, three additional cell types examined. While originally described as the damaging agent responsible for cytokine-induced ␤-cell death, these studies identify a novel role for nitric oxide as a protective molecule that promotes ␤-cell survival by suppressing DDR signaling and attenuating DNA damage-induced apoptosis.

Edited by Jeffrey E. Pessin Oxidative stress is thought to promote pancreatic ␤-cell dysfunction and contribute to both type 1 and type 2 diabetes. Reactive oxygen species (ROS), such as superoxide and hydrogen peroxide, are mediators of oxidative stress that arise largely from electron leakage during oxidative phosphorylation. Reports that ␤-cells express low levels of antioxidant enzymes, including catalase and GSH peroxidases, have supported a model in which ␤-cells are ill-equipped to detoxify ROS. This hypothesis seems at odds with the essential role of ␤-cells in the control of metabolic homeostasis and organismal survival through exquisite coupling of oxidative phosphorylation, a prominent ROS-producing pathway, to insulin secretion. Using glucose oxidase to deliver H 2 O 2 continuously over time and Amplex Red to measure extracellular H 2 O 2 concentration, we found here that ␤-cells can remove micromolar levels of this oxidant. This detoxification pathway utilizes the peroxiredoxin/ thioredoxin antioxidant system, as selective chemical inhibition or siRNA-mediated depletion of thioredoxin reductase sensitized ␤-cells to continuously generated H 2 O 2. In contrast, when delivered as a bolus, H 2 O 2 induced the DNA damage response, depleted cellular energy stores, and decreased ␤-cell viability independently of thioredoxin reductase inhibition. These findings show that ␤-cells have the capacity to detoxify micromolar levels of H 2 O 2 through a thioredoxin reductase-dependent mechanism and are not as sensitive to oxidative damage as previously thought. Although oxidative stress in pancreatic ␤-cells has been widely implicated in the pathogenesis of both type 1 and type 2 diabetes, reactive oxygen species (ROS), 6 under physiological conditions, are important signaling molecules necessary for